396 DETERMINATION OF ALKALIES IN SILICATES. 



& Co., Hatton Garden, London, to whom I have furnished all 

 the necessary directions. This shape is given it in order that 

 the portion of the crucible containing the mixture may be 

 heated strongly, while the upper portion is below a red heat. 



Manner of heating the crucible.— The ordinary crucible, if 

 used, may be heated in the manner commonly employed for 

 the fusion of silicates. If the new form of crucible, however, 

 is employed, then the upper part is grasped by a convenient 

 metallic clamp in a slightly-inclined position, and a moderate 

 blast from the table blow-pipe made to play upon it for about 

 twenty-five or thirty minutes ; but as gas is to be found in every 

 well -mounted laboratory, Bunsen burners of all dimensions 

 are used, and when properly applied can be made to give all 

 gradations of heat. A simple, cheap, and convenient furnace, 

 with a properly-arranged draught, can be made to accomplish 

 all fusions of silicates without the aid of any manual labor; 

 and I therefore employ such an apparatus. (A description of 

 it is given at the close of this article.) 



Method of analysis. — We have now the pure carbonate of 

 lime, granular sal ammoniac, and the proper crucible. The 

 silicate should be well pulverized *in an agate mortar,* and 

 half a gramme or one gramme of it is taken. The former 

 amount is most commonly used, it being sufficient and best 

 manipulated in the crucible; a gramme, however, may be con- 

 veniently employed. The weighed mineral is placed in a large 

 agate mortar, or better in a glazed porcelain mortar, of half 

 to one pint capacit}^. An equal quantity of the granular sal 

 ammoniac is weighed out (a centigramme more or less is of no 

 consequence) and put into the mortar with the mineral, and 

 the two are rubbed together intimately. After this add eight 

 parts of the carbonate of lime in three or four portions, and 

 mix intimately after each addition. Empty the contents of 

 the mortar completely upon a piece of glazed paper that ought 



* While in all mineral analyses thorough pulverization of the mineral is 

 usually essential, still it is a singular fact very good analyses can be made 

 with this method even when the powder is tolerably coarse: and in some 

 experiments with lepidolite I used powder of which much of it was in par- 

 ticles of from one fortieth to one thirtieth of an inch, and obtained excellent 

 results. Notwithstanding this, thorough trituration of the mineral is recom- 

 mended. 



